This is one of the most popular Doom source ports. It is available for DOS, Windows, Linux and Mac OS X, and should build on any POSIX platform which supports SDL. It enhances Doom with things like TCP/IP networking, OpenGL renderer, Heretic support and much more.

Hammer of Thyrion (uHexen2) is a cross-platform port of Raven Software's Hexen II source. It is based on an older linux port, Anvil of Thyrion. HoT includes countless bug fixes, improved music, sound and video modes, opengl improvements, support for many operating systems and architectures, and documentation among many others.

Dungeon Crawl Stone Soup is a free rogue-like game of exploration and treasure-hunting. Stone Soup is a continuation of Linley's Dungeon Crawl. It is openly developed and invites participation from the Crawl community. See http://crawl.develz.org !

MekHQ is a java helper program for the MegaMek game that allows users to load a list of entities from an XML file, perform repairs and customizations, and then save the new entities to another XML file that can be loaded into MegaMek.

Unknown Horizons is a 2D realtime strategy simulation with an emphasis on economy and city building. Expand your small settlement to a strong and wealthy colony and supply your inhabitants with valuable goods. LINUX PACKAGES: http://bit.ly/aurIC2

A modification of Xonotic which included extended weapons, maps, vehicles, buildable buildings, mounted weapons, spell casting, monsters, player characters, textures, and game mode (such as colorwar (think liquidwar))
To pick up items press F.
To enter vehicles/mountedguns press F.
To reload press R.
To walk press W A S D (direction)
To jump press SpaceBar
Main QuakeC repo (This is where the game code is edited):
http://chaosesqueanthology.git.sourceforge.net/git/gitweb.cgi?p=chaosesqueanthology/xonotic-data.pk3dir;a=summary
Source for the media:
http://chaosesqueanthology.git.sourceforge.net/git/gitweb.cgi?p=chaosesqueanthology/mediasource;a=summary
Other data, maps, etc are in the .iso
Dev Enviorment in tar.gz: https://sourceforge.net/projects/chaosesquedevenv/
DVD Case and DVD Labels and
Extras: https://sourceforge.net/projects/chaoseesquesupplemental/
Special thanks to NASA for images of Earth and Mars.